How to select options in Multiple select list with jQuery?

You're not going to be able to use the val method to set multiple options as selected. Instead, you should select the option itself, and set its selected attribute:

$('#uc_autori_s option[value=' + objValue + ']').attr('selected', true);

You can pass a select with multiple values an array

$("#uc_autori_s").val( $.bookAuthors );